Mercury detecting method and apparatus



March 28, 1944. P H BRAcE 2,345,090 MERCURY DETECTING METHOD AND APPARATUS Filed April 10,. 1940 v 2 Sheets-Sheet 1 g kw March 28, 1944. P. H. BRACE I MERCURY DETECTING METHOD AND APPARATUS 2 Sheets-sheaf '2 Filed April 10, 1940 INVENTO/IR vParzer' HBaae.

Patented APP r OFFICE nmrnon rus Porter 11. Brace, Forest Hills, Pa., alslgnor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa, a co ration of Pennsylvania- Application April 10, 1940, 'Serial No. 328,940

6 This invention relates to apparatus for indicating the presence of both elemental mercury vapor and mercury compounds in the atmosphere.

The detection of mercury vapor in the atmosphere is particularly important in safeguarding the health of employees in manufacturing establishments using mercury and mercury compounds. Furthermore, leaks and losses of mercury and its compounds may be quickly discovered and stopped, if suitable means are available for detecting their presence in the air.

Free mercury vapor is not the only health hazard encountered in working with mercury. Many mercury compounds are more injurious to the employees. While air having 0.02 mg. of free mercury vapor per cubic foot will injure a worker in two or three months, a much smaller quaizitity of mercury compounds, particularly the mercuric salts, will be harmful in a shorter time. There is some medical authority to the eflect that in the final analysis it is the mercury compounds, and not free mercury,- that constitute the principal hazard to human beings.

There has been very little done to detect and indicate the existence of mercury compounds as dusts and suspensions or even sublimations in air breathed by workers. An indication of the presence of only free mercury in the air does not necessarily give a, complete or true indication of the hazard to those coming into contact with mercury contaminated air.

The object of this invention is to provide for detecting both elemental mercury vapor and suspensions of mercury compounds in the atmosphere and for registering the amount of such mercury vapor and mercury compounds.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises th features or construction, combinations of elements and arrangement of parts which will be exemplified in the construction hereinafter set forth, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings, to which:

Figure 1 is a view in perspective of one form of the apparatus constructed in accordance with the invention:

Fig. 2 is an enlarged sectional view taken on the line l'I-lI of Fig.1;

Fig. 3 is a view, partly in section, of a second modification oi. the invention;

Fig. 4 is a sectional view of a third modification of the invention:

Fig. 5 is a sectional view of a fourth modification of the invention; and

Fig. 6 is a plan view looking at the top of Fig. 5.

In the prior art, there are several methods of detecting and indicating the presence of free .mercury vapor in air. These methods will be more fully illustrated in conjunction with the several forms of myinvention to be hereinafter described.

It is a purpose of my invention to detect and indicate the presence of mercury compounds, as well as free mercury vapor, v

Certain mercury co pounds dissociate into free mercury vapor upon eating to temperatures of about 500 C. and higher. Examples of such compounds are the mercury oxides, mercuric sulphide and mercuric chloride. Heat alone is in sufficient to break down many other mercury compounds. However, it has been discovered that substantially all mercury. compounds when strongly heated in the presence of lime will dissociate to free mercury almost quantitatively. My invention is predicated on the use of heat, with or without lime, in order to dissociate mercury compounds suspended in air into free mercury.

Turning to Fig. 1 01' the drawings, there is illustrated in perspective an apparatus suitable for detecting and indicating both free mercury vapor and mercury compounds present in the air, either separately or as a total.

This apparatus comprises a cabinet It having a right sid wall I I, a left side wall 82, bottom tion 2|, and joining therewith a vertical partition 22. The vertical partition 22 has a small window or aperture 23 therein. The cover It is so constructed that when closed against cabinet In, the compartment formed by walls 2|, 22 and the cabinet I0 is efl'ectivelyisolated from the rest of the apparatus in casing l0. Sealing means,

Such as rubber gaskets or the like on cover it,

may be employed for this purpose. Thereby the compartment formed by walls 2|, 22 is substan-.

The tube 25 is fastened at each end in aperturesin the side walls and I2. The tube 25 may be welded or joined in any suitable manner. A refractory inner tube 25 is disposed in the tube 25 and spaced therefrom by insulating members 31..

A small air intake member 21 extends into the refractory tube 26. The air intake member 21 has an intake opening 28 adjacent the wall ii, and near this opening it is surrounded by an electrical heating coil 29.

Within the air intake tube 21 in the zone heated by coil 23, is located a porous plug 25, shown in Fig. 2, preferably of lime, or some mineral such as calcium carbonate, which upon heating will decompose and produce lime. The porous plug 24 heats the air passing therethrough and dissociates mercury compounds, and also acts to filter out dust. An electrical thermostat 3B in coil 29 controls the heating effect thereof.

The intake member 21 extends beyond the left wall [2 of cabinet Hi to the exterior, and carries a series of cooling fin members 33 on this exterior portion. The intake tube 21 reenters. the cabinet through wall I 2 at a higher elevation and terminates in an exhaust port 34. This exhaust port is within the compartment formed by walls 2 l, 22.

Attached to the vertical wall 22 external of the compartment, but within the cabinet I0, is a carrier case for holding a supply of translucent or transparent selenium sulphide strip 32. A cover 35 is retained in position on the case 35 by a wing nut 31 threaded on a post 38. A guide 39 for selenium strip 32 extends from carrier case 35 and terminates at a window adjacent window or aperture 23 in the wall 22.

A second guide 43 above the aperture 23 extends from a cylindrical receiving case 4| for receiving used selenium sulphide strip. A winding spindle 42 is rotatably mounted in the case 4|. The winding spindle 42 has attached thereto a worm gear 43 which meshes with a worm 44 on a driving shaft 45 rotatably mounted in bearings 46 and 41. The end of shaft 45 remote from worm 44 has mounted thereon a gear 48 meshing with a slow-speed driving gear 49 which is part of a speed-reducing mechanism 5|. The speed-reducing mechanism 5| is driven from an electric motor 50. 1

A second shaft 52 carrying a fan 53 extends from the speed-reducing mechanism 5 l. Shaft 52 is preferably driven at about motor speed, whereby fan 53 may be effective in withdrawing air from the compartment formed by walls 2|, 22. An opening 54 is provided in upper wall 14 of the casing in order to accommodate the fan 53 and permit the escape of air. I

Within the compartment formed by walls 2|, 22, is a lamp housing 55 fastened to wall l2. Within the housing 55 is located a bulb 51 electrically connected at 58 to conductors 53. Conductors 59 are connected to a source of energy 56 which supplies energy both to motor and to lamp 51. At the end of the housing remote from its connection to wall I2 is a condensing lens 50 which focuses the light from lamp 51 substantially at the window 23.

On the opposite side of window 23 from the lamp housing is a photo-sensitive cell 62, mounted on bracket 53, provided with a tube 5! carrying a, set of light collecting lens. Electrical impulses from photo-cell 52 are conducted by means of conductors 64 to a suitable indicating mechanism 65 carrying a pointer 51 and a scale 66.

Current from the source 55 is conducted both to the lamp and electric motor by wiring 59. Other wiring 69 conducts the current to a switch 53 which controls current, flow to the heating coil 29 and thermostat 30.

The apparatus operates in the following manner: The cabinet I0 is located in the place whose atmosphere is to be tested for presence of free mercury vapor and mercury compounds. A source or current 55 is connected to the wiring 59, 69, and the heating coil 29 is brought up to a predetermined temperature. A quantity of air is drawn in at 28 of the air intake tube 21 through the zone heated by coil 29 due to the eflect of fan 53. Air coming into contact with the porous plug is heated to a high temperature. Mercury in compound'form will react with the lime and dissociate to release free mercury vapor. Also any soot, dust or the like will be filtered out by the porous plug. The gases travel along air intake tube 21 to the cooling portion 33 where their temperature is reduced. The mercury will remain in its elemental fomi after cooling. The air from intake tube.'2 1 escapes at outlet 34 where it impinges against the selenium sulphide strip 32 at the window 23.

The: effect of mercury upon the selenium sulphide strip is to cause darkening and opacity of strip 32 proportional to the quantity of mercury vapor present. The light from lamp 51, focused by lens 60 is projected upon the selenium sulphide strip 32. The amount of light traversing the strip 32 will be collected by the lens 6! and converted into current by the photo-sensitive cell 62 and transmitted to the indicating mechanism 85. The pointer 51 is adjusted to give a zero reading with undarkened or freshsulphide strip. Any darkening of the strip of selenium sulphide will diminsh the amount of light transmitted to the photo-sensitive cell, and thereby effect a change in the reading of the indicating instrument 65.

It is preferable to place theexhaust 34 so that the escaping air acts on the selenium sulphide paper almost at the focus of the light from lamp 51. The winding mechanism 43, 44, 48, 39, etc., constitutes a considerable reduction in speed for motor 50, and the selenium sulphide strip 32 travels past window 23 at a rate of only a few inches an hour. The speed may be varied to suit conditions.

Any given portion of the strip may be exposed for any predetermined period of time, and indicates almost quantitatively the amount of mercury in the air for such predetermined period of time. Therefore, the strip 32 may be examined visually after removing from it receiver casing 4|. Visual comparison with suitable standards will indicate the quantity of mercury and mercury compounds in the air.

There are several methods of operating the mechanism of Fig. 1 in order to obtain several different types of indication. If coil 23 isnot operatedthat is, the intake is run cold-then the apparatus records only the amount of elemental mercury vapor in the air,'and does not record the presence of any mercury compounds. When operated hot, the mechanism records the total of both mercury vapor and mercury compounds. A subtraction will indicate the quantity of mercury compound present in the air. It is feasible to operate the mechanism on five or ten-minute hot and cold cycles, and thereby have a continuous determination of the respective amounts of both types of mercury.

The lime plug will make the instrument of universal utility in establishing the quantity of both free mercury and mercury in compound form in the air. As previously described, certain mercury compounds dissociate simply under heat. It the apparatus is to be used in locations known to be subject to the presence of the latter types of mercury compounds, such as the oxides or the sulphide, then any refractory porous material may be used within tube 2'Ifor example, aluminum oxide or silicon carbide would be suitable plug materials. The same plug construction is employed in each of the other modifications of my invention, as is hereinafter described.

In place or a simple indicator, such as 65, which must be scanned by the operator from time to time to see it harmful concentrations of mercury are present in the air, it would be equally feasible to install a recorder type of mechanism. A traveling chart would replace stationary scale 66, while pointer 61 would apply ink to the moving chart.

In the modification of Fig. 3, the principle of operation is based upon the absorption of light of specific wavelengths by mercury vapor, particularly at 2537 angstroms. This is a wellknown phenomenon, and has proved effective for detecting minute quantities of mercury vapor.

An air intake tube I admits-air to a plug 12 heated by an electric coil II. .Mercury vapor present in the air is drawn into chamber 13 at the exhaust end of tube I0. The chamber I3 has a window 10 of quartz, or other suitable material, fastened by a'ring I5 totube I0. A light source emitting light of wavelengths ab sorbable by mercury vapor is located at I6. The type of light bulb used for this purpose should be rich in light of wavelengths of 2537 angstroms. A low mercury vapor pressure lamp is satisfactory.

The other end of the chamber I3 is closed by a quartz disc 'II secured by a ring I8 to chamber I3. A photo-sensitive cell I9 records the amount of light passing from light source I6 through the chamber I3. Conductors 80 connect the photo-sensitive cell to a suitable indicator 8!, which may be of the pointer type, as shown, or a recorder.

The presence of even small quantities of mer- .cury vapor within chamber I3 will result in a proportional absorption of considerable amounts of the light emitted by lamp I6, and thereby the indicator 8i operated from the photo-sensitive cell I9 will indicate the relative amount of mercury vapor present.

An exhaust jacket 82 encloses a fan 84 driven by motor 93 which draws gases through the apparatus. It is not necessary to cool the mercury vapor after it has passed through the heated plug I2.

In the modification of Fig. 4, the air intake tube 90 carries a porous plug 92 heated by coil 9|, whereby mercury compounds may be dissociated to give free mercury vapor. Cooling fins 93 reduce the temperature of the air which has been heated at plug- 92.

Attached to the exhaust end of tube 90 is a ries some reagent which is chemically sensitive to the presence of free mercury vapor. Selenium sulphide is a suitable reagent. There are numerous others. A scale 96 indicates the depth of discoloration of the mineral, and the observer may examine the porous mass 95 through the transparent sleeve 96, and by comparison with the scale 96 i given an indication of how much mercury vapor is present in the air. The time necessary to produce a given zone of discoloration will indicate the concentration of the mercury in the air. I

An exhaust Jacket 91 within which a fan 98 is operated by the motor 99 effects movement of the air from the intake and through the apparatus.

A form of apparatus requiring no motor is illustrated in Figs. 5 and 6. This apparatus dependsupon its operation forthermal currents. The air intake tube I00 is located vertically. Air

entering the tube is heated by the porous plug.

I02 and coil IIII. The heated air rises readily. A small cooling fin area I03 reduces the temperature of the gases somewhat. The rising air impinges upon a horizontally placed-cover member I06 spaced a small distance from the flared exhaust end I00 of the tube. The cover I06 is pivotally mounted at I05 to the flared exhaust end I04 of the tube I00.

On the underside of the cover I06, as shown in solid lines in Fig. 5, is' placed a mercury vapor sensitive strip I01. This sensitive strip may consist of a coating of selenium sulphide reagent on paper. The observer may let the apparatus operate for a suitable periodof time with the cover placed in operative position, and then he may tip back the cover to the dotted line position of Fig. 5 and observe the depth of staining of the selenium sulphide by any mercury vapor in the air.

For the purpoe of determination of concentrations of mercury vapor and mercury compounds in the air, a suitably graded check strip I08 prepared under controlled conditions may be placed on the strip I01, and by noting the strip portion having equal depths of the discoloration it may 'be quickly determined what the concentration of mercury is in the air. a

Since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting vapor, a cooling means in association with the intake member beyond the heating means to reduce the temperature of the heated air from the air intake member, and means sensitive to the presence of mercury vapor disposed adjacent the outlet end of the intake member in position to be impinged upon by the cooled air to indicate the presence 01 any mercury vapor in the cooled air.

2.. An apparatus for indicating the amount of elemental mercury vapor and mercury compounds present in air comprising an air intake tube having a porous plug therein composed of lime adjacent the air entry end thereof and heating means associated with the porous plug providing for heating air passing therethrough to a tem perature of above ciation of mercury in compound form into tree mercury vapor, cooling means associated with the air intake tube to cool the air beyond the .porous plug, means sensitive to the presence of mercury vapors associated with the tube beyond the cooling means, including a strip of translucent material coated with a mercury vapor sensitive substance adapted to be rendered opaque in proportion to the amount 01' mercury vapor in air applied thereto, the tube terminating adjacent the strip and directing the air thereagainst, means for projecting a beam of light against the strip of material and a photo-sensitive cell positioned to receive the light, beam from the strip to indicate the opacity of the strip of material, and means to move the strip at a predetermined rate past the terminus of the tube and means to efiect flow of air through the air intake tube.

3. An apparatus for indicating the amount of elemental mercury vapor and mercury compounds present in air comprising an air intake tube having a porous plug therein adjacent the air entry end thereof and heating means associated with the porous plug providing for heating air passing therethrough to a temperature 01 above about 580 C. to cause dissociation of mercury in compound form into free mercury vapor, cooling means associated with the air intake tube to about 500 C. to cause disso-.

assaooo cool the air beyond the porous plug, and means sensitive to thepresence oi mercuryvapors disposed adjacent the outlet end of the intake tube sothat air from the coolingmeans impinges thereon, said sensitive means including a member carrying a mercury sensitive substance which changes its appearance in proportion to the amount of mercury vapor in the cooled air.

a. The method of detecting both free mercury vapor and mercury compounds in air which comprises passing the air through a porous reiractory material .at elevated temperatures so as to convert substantially all or the mercury compounds to free mercury vapor, and then determining the proportion of mercury vapor in the air.

5. The method of detecting both free mercury vapor and mercury compounds in air which comprises passing the air through a porous lime material at elevated temperatures of the order of 500 C. so as to convert substantially all of the.

mercury compounds to free mercury vapor, and then determining the proportion of mercury vapor in the air.

6. Apparatus for detecting both mercury vapor and mercury compounds in air which comprises a tube having an air-intake and an air-outlet,

means sensitive to mercury vapor adjacent the air-outlet and positioned to be contacted with air therefrom, a refractory porous plug within the tube and adjacent to the air-intake, high temperature heating means associated with the porous plug for heating the same, and cooling means for the air between the porous plug and the means sensitive to mercury vapor.

- PORTER H. BRACE. 

